Optical circulator is an important optical device with the anti-interference function in integrated optics. The optical circulator can realize circular light transmission in single rotational direction among a plurality of ports, so that incident signals can smoothly pass through while reflective signals can be isolated. Due to the characteristic, the optical circulator can greatly reduce the mutual crosstalk of reflective light of devices in an integrated optical circuit and is highly favorable to improve the system stability. The traditional optical circulator is mainly based on the block structure of magneto-optical materials and has the disadvantages of large volume and difficulty in integration with other optical devices. The disadvantages greatly limit the application of optical circulators in a new generation of optical devices.
The introduction of the concept of photonic crystal and the research and development of photonic crystals provide new thoughts and methods for the implementation of easily integrated small-size magneto-optical circulators. Photonic crystal is a novel artificial material formed by the periodic or quasi-periodic arrangement of different dielectrics. One important characteristic of the photonic crystal is the existence of photonic forbidden band, and waves within the corresponding forbidden frequency band cannot be propagated in the crystal. The control and operation of photons can be realized by the introduction of defects in the photonic crystal by utilizing the band gap effect. Devices with different functions, based on the unique optical property of the photonic crystal, have been widely developed and applied. For example, photonic crystal lasers, photonic crystal wavelength division multiplexer/demultiplexer, photonic crystal resonant cavities and photonic crystal switches. The devices have immeasurable application prospects in novel photonic crystal devices.
The photonic crystal circulator designed by utilizing the magneto-optical effect has the advantages of compact structure, flexible design and very large scale in integration, and has potential application value in the aspect of improving the signal stability of a photonic crystal device integrated system. However, the study of photonic crystal magneto-optical circulators is still in the preliminary stage, and the photonic crystal magneto-optical circulators all adopt the structural design based on a single photonic crystal magneto-optical cavity. Due to the single-cavity nature in the structure, these photonic crystal magneto-optical circulators have certain limitation in the aspect of port expansion.